In connection with oil spill protection operations where one has tried to use traditional oil booms and skimmers in order to collect oil from the sea surface, it has proven difficult to keep the oil in the oil boom long enough for the skimmer to transfer it to a tanker or the like. The reason is that if the relative velocity between the boom and the water exceeds about 1 knot, the oil has a tendency to escape below the boom. This situation is aggravated in waves, and even the best of the existing oil booms will in reality have problems in keeping the oil contained in wave heights above 3 meters.
In order to alleviate these problems, an oil collecting system has previously been suggested in DE-A-2936151 where one can transfer the oil continuously from the boom to a floating, generally closed separation container which is towed behind the boom and is connected to an opening at the bight of the boom by means of a tubular member. The separation container is in the bottom provided with one or more openings so that water can escape, and the container is sufficiently large for any mixture of oil and water to have sufficient retention time to undergo a gravity separation. As the container is filled with oil, it may be emptied over into a trailing collection container.
A disadvantage in the system according to DE-A-2936151 is that the towing forces of the separation and collection containers are transmitted directly to the oil boom via the tubular member. These forces have an impeding effect on the ability of the oil boom to follow the motions of the sea. Furthermore, motor driven propellers are arranged both in the tubular member and in the connection between the separation and collection containers in order to provide transportation of the water and oil. These propellers will cause a strong stirring and mixing of the oil and water that will complicate the desired separation of these liquids.
In order to avoid or reduce these problems, it is suggested according to the invention to modify the previously suggested system in such a way that the tubular member will function as a pump under the influence of the wave motion of the water.
This is obtained according to the invention by forming the tubular member in a flexible manner so that it will be able to follow the wave motion of the water and thereby act as a pump, for instance by it being provided internally with means restricting the flow therein from the boom towards the collection container. Such means can be non-return valves of different shapes, so that a kind of peristaltic effect is obtained.
In order for the tubular member, in the following also called the pumping hose, to be able to follow the motions of the sea as efficiently as possible, it is suggested according to the invention to transmit the necessary towing forces to the collection container by means of separate tension members. The tension members can be run from the collection container to e.g. a point on the boom spaced from its opening, or directly to a towing vessel.
The length of the tension members is preferably adjustable, i.a. in order to make the excess length or the slack in the pumping hose variable for the adjustment to the prevailing wave conditions, i.e. the length and height of the waves.
The expected wave length will also influence the length of the pumping hose, this length being preferably at least one half of the wave length of the longest waves to be expected to some extent.